The present invention is directed to an expansion dowel including an anchor bolt having a axially extending cylindrical shank with an expansion part at one end and means at the other end for securing a member to a receiving material into which the dowel is anchored. At least an axially extending portion of the anchor bolt shank is enclosed by an expansion sleeve displaceable relative to the bolt. The expansion sleeve has at least one axially extending slot open at its end closer to the expansion part and it is provided on its outside surface with radially projecting protrusions.
Expansion dowels of this type are used for securing workpieces to a receiving material such as a structural component, where a bore in the component and a bore in the workpieces are similarly dimensioned, so that after the workpiece is arranged in the desired attachment position, the expansion dowel can be pushed through the bores aligned with one another. By turning engagement means, such as a nut with a suitable tool, the expansion part on the anchor bolt is pulled into the expansion sleeve whereby the sleeve anchors itself in the structural component when it is expanded by the expansion part.
A dowel is disclosed in GB-PS 1 333 893 where the anchor bolt is located at the inner end of the expansion sleeve and, upon installation, the expansion sleeve is forced outwardly at the base of the bore. The expansion dowel is made up of an elongated cylindrical anchor bolt with a conically shaped expansion part at one end and a widenable expansion sleeve positioned on the anchor bolt. The expansion sleeve has protrusions stamped outwardly from the inside of the sleeve. The protrusions are arranged so that they project outwardly from the largest circumference of the anchor bolt or expansion sleeve.
The expansion force developed after the expansion dowel has been set, produces essentially a friction force of equal magnitude between the anchor bolt and the expansion sleeve and between the borehole surface and the expansion sleeve. As a result, such an expansion dowel has an extremely unfavorable re-expansion character, for instance, in a fractured or broken tension zone in the receiving material, since displacement of the anchor bolt relative to the expansion sleeve cannot be assured. Due to the basically equal frictional forces, the expansion sleeve can move together with the anchor bolt relative to the bore hole surface. The protrusions on the expansion sleeve serve for stationary retention of the expansion sleeve in the borehole when the expansion dowel is being anchored. These protrusions are not located on the radially expandable region of the sleeve and, accordingly, do not fulfill the corresponding holding function in the fractured tension zone.
Additionally, it is known that expansion dowels of this type, formed of stainless steel, tend to "corrode or wear" between the anchor bolt and the expansion sleeve. Especially with expansion dowels used where the tension zone can fracture, it is important to avoid this "corroding phenomenon" to assure a secure re-tightening in the fractured zone.